Tanning agent and process



2,829,943 Patented Apr. 3, 1%58 2,829,943 TANNiNG AGENT AND PnocEssEdward M. Filachione and Edward H. Harris, in, Philadelphia, Pa.,assignors to the United States of America as represented by theSecretary of Agriculture No Drawing. Application January 24, 1956 SerialNo. 561,163

9 Claims. (Cl. 8-94.33) (Granted under Title 35, U.-S. Code (1952), sec.266) A non-exclusive, irrevocable, royalty-free license in the inventionherein described for all governmental purposes, throughout the world,with power to grant sublicenses for such purposes is hereby granted tothe Government of the United States of America.

This invention relates to the tanning of hides andskins and to theleather thus produced.

An object of this invention is to provide novel tanning materials andprocesses. Another object is to provide leather having new and improvedproperties; in particular, leather that retains leatherlike propertiesafter being heated above its shrink temperature and that shrinksreversibly when so heated.

The shrink temperature of leather is intimately related to the type anddegree of tannage used in its preparation. Untanned hides have a verylow shrink temperature (about 60 C.) and, when heated at or above thistemperature in the presence of water, shrink irreversibly to yield ondrying a hard, horny, translucent product having no resemblance toleather. Conventional tannage yields leather of somewhat elevated shrinktemperature. If heated above such temperature, however, itshrinksirreversibly and becomes hard and stiff, thus becoming useless for mostpurposes.

Accordin to the invention, a new t e of leather is made by applying atanning composition, preferably 211- kaline, containing as the tanningagent a polyglycidyl ether of glycerol, preferably in aqueoussuspension, to hides, skins, or pretanned leather until they are tanned.These tanning agents are conveniently made by condensing epichlorohydrinwith glycerol according to well known procedures, such as thosedescribed in U. S. Patents 2,5 81,464 and 2,633,458. They are a mixtureof glycidyl ethers having the general formula wherein R is a glycerylresidue, at is l to 2, y is 1 to 2, z is 1 to 2 and x+z=2 to 3. It is tobe understood that since these materials are complex mixtures and arepolymeric in nature, the above formula represents only their averagecomposition.

Since glycerol is trifunctional, it can react with three moles ofepichlorohydrin, thus thus giving rise to branched-chain or evencrosslinked products. It is believed that this actually occurs to acertain extent, either in the preparation of the polyglycidyl ether orin the use of the latter as a tanning agent, or both, and that theunique tannage achieved in the practice of the invention is directlyrelated to this ability of the polyglycidyl ether to form branchedand/or cross-linked chains. This view is substantiated by the fact that,of the many monoand di-epoxides that have been used or suggested for usein tannage, none has been observed or reported to give the uniquevaluable properties achieved with the glycerol polyglycidyl ethers ofthis invention.

Hides, skins or pretanned leather, after being tanned with ourpolyglycidyl ethers of glycerol, not only show the usual valuableproperties imparted by conventional tannages but in addition showseveral distinctive new and useful properties. The most startling newproperty is the behavior of the leather when exposed to steam or hotwater. Ordinary vegetable tanned leather has a characteristic shrinktemperature of about 80 C. and if heated above this point undergoesirreversible shrinkage such that after it is cooled and dried it isshrunken, warped and misshapen and is also hardened, stiffened andembrittled so that it no longer has leatherlike properties. In contrast,when leather tanned by the process of this invention is heated above itsshrink temperature, although it shrinks somewhat, the shrinkage isreversible and the article recovers substantially its original shape anddimensions upon being cooled. Of equal importance, it retainssubstantially its original shape, feel, flexibility and other usefulproperties. Another highly valuable property of leather tanned by ourprocess in. its ready wettability. in the commercial processing ofhides, skins and leather occasions frequently arise where it isnecessary to rewet them after they have been dried. Frequently suchrewetting is a slow and tedious process and often the efiectiveness ofthe subsequent treatment is impaired by the rewetting having been unevenor incomplete. We have found that hides, skins and leather treated byour process rewet with great speed and uniformity. Frequently this caseof rewetting is a valuable property in the finished leather product, asin chamois leather for instance. Where it is objectionable it is easilycounteracted by conventional treatment of the leather with oils, waxes,or other hydrophobic agents. Another advantage of tanning by our process is that a White leather is produced thus eliminating various stepsin conventional white leather manufacture, such as bleaching and/orfilling with white pigments. Furthermore the leather is white throughoutits entire thickness in contrast to bleached and/ or pigmented whiteleathers. Also the leather produccdby our process is completelyresistant to detannage by means of acids, alkalies and other agents andhence is more stable than conventional mineral and vegetable tannedleathers.

Our process of tanning can be carried over a wide range of conditions.The pH range can be varied widely, however, we prefer to carry out theprocess in alkaline solution preferably in the pH range of about 8 to12. If desired inorganic salts may be used as in conventional tannerypractice to control osmotic pressure but are not essential for tanningto be effected. Our process can be carried out in organic solvents suchas the lower ketones and ether alcohols or mixtures of these with water.However, we prefer to use aqueous systems because of the greater costand hazards of organic solvents. 'If desired surface active agents maybe used in our process to increase the rate of tanning.

The practice of the invention is illustrated by the following examples.

Example I Pickled cowhide was depickled by a one day immersion in 5%aqueous solution of sodium bicarbonate. After being rinsed with water,15 g. (dry weight) of the wet hide was rolled in a jar mill togetherwith a suspension of 10 g. of a glycerol polyglycidyl ether in 200 ml.of water. The polyglycidyl other had an epoxide equivalent of about andits average composition corresponded to the structural formula abovewherein x, y and z had values of about 1, l and l. After two days in thejar the pH ofthe liquid, originally 8.1, had dropped to 6.9. The hidewas rinsed with water and its shrink tempera.

Example II A 20 g. (dry wt.) sample of the used in Example I was treatedas in Example I with 10 g. of the same glycerol polyglycidyl ether in100 ml. of water, the significant difference being that a wetting agentwet depickled hide polyglycidyl ether used in Example I and 100 ml. ofwater or 0.2 M aqueous buffer solution. The various treatments are shownin the table below at regular time intervals the pH of the liquor andthe shrinkage temperature (Ts) was determined with the results shown inthe table. As expected calfskin was tanned more rapidly than cowhide, aleather showing reversible shrinkage being obtained after 8 hours oftanning (Examples XII to XIV). Cowhide required one or more days,excepting when treated in the presence of lime, to give a leathershowing reversible shrinkage (Examples VI to XI).

Shrinkage temp., 0., after Example Buffer Salt, percent pH 8 hrs. 24hrs. 48 hrs. 72 hrs. 96 hrs.

Cowhide VI Na lactate. 0.2 M 6. 4-7. 8 65 71 75 77 77 VII None (H2O)None" 5. 8-7. 3 66 69 77 80 79 VIII NaHCOs. 0. M 8. 1-8.3 68 74 75 77 76IX NarCOa, 0.1M 9.9 74 80 78 80 83 XI Ca(OH)z, Silt. Na2SO4, 10---- 10.8-11. 1 79 78 86 86 Calfskin:

XII--." NazCOz, 0.2 M NfizSOi, 10---. 10.2 81 85 85 87 86 XIII MgO.1 aNa2S04,10- 10.2 78 85 85 85 XIV---" Oa(OH 2, Sat NazSO4, 10.--.10.2-11.3 85 87 88 89 was used (1 g. of sodium lauryl sulfate). After 24hours in the jar mill the sample was removed, rinsed and evaluated. Itsshrink temperature was 80 C. After 1 minute in boiling water it wascooled, whereupon it regained its original dimensions and appearedidentical to the product of Example I.

Example III A sample of pickled grain split steerhide was depickled,brought to its isoelectric point, and dehydrated by immersion in twochanges of acetone. A g. sample of the dehydrated steerhide was thentreated with a solution comprising 10 g. of the glycerol polyglycidylether used in Example I in 90 ml. of ,B-methoxyethanol diluted with 10ml. of water which solution contained 0.5 g. of sodium carbonate. After4 days the hide under treatment was removed, rinsed twice with acetoneand washed in water. The shrinkage temperature of the leather was about80 C. and the original dimensions were regained upon cooling theshrunken leather.

Example IV A sample of pickled calfskin was depickled and tanned withthe same glycerol polyglycidyl ether and the same procedure as inExample I except that the aqueous suspension of tanning agent contained10% of sodium chloride and was 0.2 molar with respect to sodiumcarbonate. The tanned leather had a shrinkage temperature of 80 C. evenafter a treatment for only 8 hours. The shrinkage caused by boiling inWater for 1 minute was fully recovered on cooling and all characteristicleather-like properties were retained after such treatment.

Example V A sample of the depickled cowhide used in Example I wasrelimed by soaking it for 24- hours in saturated lime water. The hidewas then tanned as in Example I. After one day of treatment the pH ofthe liquid remained at about 9. The treated hide was Washed in water andfound to have a shrinkage temperature of 80 C. The leather showed thesame reversibility of shrinkage as that in Example I.

Examples VI-XI V A series of experiments was run to show the rate oftannage under various conditions.

Pickled calfskin and cowhide were depickled by immersion in 5% aqueoussodium bicarbonate solution, rinsed, brought to the isoelectric point(pI-I about 5) and then washed to remove salts. Samples of about 10 g.(on a dry basis) were placed in bottles with 5 g. of the glycerol In allof the treatments the maximum shrinkage temperature was reached in aboutthree days or less. The fully tanned leathers were white, firm andflexible, and all showed the reversible shrinkage when heated in boilingwater that is characteristic of the invention.

Example XV Grain split steerhide, split out of the lime, was obtainedafter the conventional liming, unhairing and splitting bearnhouseprocess. The split steerhide was delimed with an acetic acid-sodiumacetate solution (pH about 5) and washed. The drained hide, 90 g. on adry basis, was added to 875 ml. of an aqueous solution which was 0.2molar with respect to sodium carbonate and contained 87 g. of sodiumsulfate. Then 45 g. of the glycerol polyglycidyl ether used in Example Iwas added and the tanning carried out at room temperature by rolling thecontents in a bottle placed on a jar mill. After one day of treatmentthe steerhide was removed and thoroughly washed in water. The shrinkagetemperature of the leather was 85 C. and the shrinkage was reversible.The leather when air dried showed a gain in weight of 14%.

The grain split steerhide tanned as above with glycerol polyglycidylether was retanned with a blend composed of two thirds sulfitedquebracho extract and one third chestnut extract in aqueous solution inthe conventional manner. After 4 days the vegetable tannin hadcompletely penetrated. The shrinkage temperature of the retanned leatherwas 91 C. and the gain in weight upon retanm'ng with the vegetableextract was about 50%.

Example XVI the initial value of 60 to 71 C.; after 8 hours it was 76and after 32 hours it was Longer treatment caused no further change. The4 and 8 hour samples showed excellent leatherlike properties andrecovered almost their original dimensions after being boiled inwaterfor 1 minute. The 32 hour sample was completely tanned and showedsubstantially full recovery from heat shrinkage without any apparentloss of its leatherlike properties.

While in the above examples the tanning agent used was :1 glycerolpolyglycidyl ether having an average composition corresponding to theformula shown above in which x, y, and z had approximate values of 1, 1,and 1 respectively, equivalent results are obtained when similarglycerol polyglycidyl ethers in which x, y and 2 have values in theranges 1-2, l-2 and l-2, respectively, are used, provided x+z is in therange 2-3.

Leather tanned according to the invention is suitable for use with anyof the conventional finishing agents and processes. The process of theinvention is applicable not only to the cowhide and calfskin used in theabove examples but also to any hide or skin commonly used for tannageexcept the fur skins. The term hide, as used in the appended claims,includes all such hides and skins.

A combination tannage, in which the tannage with glycerol polyglycidylether either precedes or follows a conventional tannage, especially avegetable tannage, is particularly advantageous when a highly tannedleather is desired.

We claim:

' l. A process of tanning hides comprising applying to the hides atanning composition containing as the tanning agent a glycerolpolyglycidyl ether corresponding to the formula [OOHPCETCIL O l 2Cl \o/1| wherein R is a glyceryl residue, x is 1 to 2, y is 1 to 2, z is l to2, and x+z is 2 to 3 until the hides are tanned.

2. A process of tanning hides comprising applying to the hides analkaline tanning composition .containing as the tanning agent a glycerolpolyglycidyl ether corresponding to the formula CHzOl 0 I wherein R is aglyceryl residue, x is 1 to 2, y is 1 to 2, z is 1 to 2, and x+z is 2 to3 until the hides are tanned.

3. A process of tanning hides comprising applying to the hides analkaline tanning composition .containing as the tanning agent a glycerolpolyglycidyl ether corresponding to the formla [ocHr-cH- om] R'/ 0 I OCHCH --00H OH-CH l-(g 2- 2] H201 0 wherein R is a glyceryl residue, x is 1to 2, y is 1 to 2, z is 1 to 2, and x-I-z is 2 to 3 in aqueoussuspension until the hides are tanned.

4. The process of claim 1 wherein x, y, and 2 each has a value of about1.

5. The process of claim 2 wherein x, y, and z each has a value of about1.

6. A process of tanning hides comprising tanning said v 6 hides with avegetable tanning agent and thereafter applying to the resulting hides atanning composition containing as the tanning agent a glycerolpolyglycidyl ether corresponding to the formula \[(OCH2-(IJH )OGH2CCH2 OsOl 0 1 wherein R is a glyceryl residue, at is l to 2, y is l to 2, z isl to 2, and x+z is 2 to 3 until the hides are tanned.

7. A process of tanning hides comprising tanning said hides with avegetable tanning agent and thereafter applying to the resulting hidesan alkaline tanning composition containing as the tanning agent aglycerol polyglycidyl ether corresponding to the formula [0 CHFOE7CH2] OI 0 R\ OGHa-CH OCHz-OH-CH2 I l l C 2Cl y 0 wherein R is a glycerylresidue, x is 1 to 2, y is 1 to 2, z is 1 to 2, and x-l-z is 2 to 3until the hides are tanned, and then retanning the resulting hides witha vegetable tanning agent.

9. A process of tanning hides .comprising applying to the hides analkaline tanning composition containing as the tanning agent a glycerolpolyglycidyl ether corresponding to the formula [0 Offs-(33701111 0wherein R is a glyceryl residue, at is l to 2, y is l to 2, z is 1 to 2,and x-l-z is 2 to 3 in aqueous suspension until the hides are tanned,and then retanning the resulting hides with a vegetable tanning agent.

References Cited in the file of this patent UNITED STATES PATENTSImmendoerfer Aug. 31, 1937 OTHER REFERENCES Immendorfer, Das Leder 4,page 229 (1953).

1. A PROCESS OF TANNING HIDES COMPRISING APPLYING TO THE HIDES A TANNINGCOMPOSITION CONTAINING AS THE TANNING AGENT A GLYCEROL POLYGLYCIDYLETHER CORRESPONDING TO THE FORMULA